Light source device and display device

ABSTRACT

A light source device includes a discharge tube, a reflector for reflecting a light radiated from the discharge tube, and support members for supporting the discharge tube to the reflector. The support member or the discharge tube is formed of a heat insulating structure so as to prevent a temperature drop of a portion of the discharge tube near electrodes thereof. By this arrangement, it is possible to prolong the operational life of the discharge tube.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of PCT/JP 02/02622 filed Mar.19, 2002, which claims the priority of Japanese Application No.2001-078546 filed Mar. 19, 2001, which is incorporated herein byreference.

TECHNICAL FIELD

[0002] The present invention relates to a light source device having adischarge tube emitting light by a discharge in a lean gas.

BACKGROUND ART

[0003] A backlight, as a light source device of a display device such asa liquid crystal display device, uses a light source device comprisingone or a plurality of discharge tubes and a reflector. The dischargetube is a cold cathode tube, in which mercury is contained in a lean gas(such as Ar and Ne) and a fluorescent material is coated on the tubewall. Electrodes are provided in both ends of the discharge tube. Thedischarge tube is supported by the reflector with support members whichare arranged at positions near the electrodes of the discharge tube. Thebacklight also has a light guide plate, and the light source device isarranged on the side of the light guide plate.

[0004] When the high voltage is applied to the electrodes of thedischarge tube, electrons are emitted by the electrodes and impingeagainst the mercury gas in the discharge tube. The mercury gas producesultraviolet light, which impinges against the fluorescent material inthe discharge tube to emit visible light. As the amount of the mercurygas in the discharge tube is reduced, the amount of emitted light isreduced and an operational life thereof ends. Usually, a sufficientamount of mercury gas is sealed in the discharge tube to enable thedischarge tube to have a long life, but there are discharge tubes havingextremely short operational lives.

SUMMARY OF THE INVENTION

[0005] The object of the present invention is to provide a light sourcedevice capable of a long operational life of a discharge tube.

[0006] A light source device, according to the first aspect of thepresent invention, comprises a discharge tube, a reflector forreflecting a light radiated from the discharge tube, and support membersfor supporting the discharge tube to the reflector, said support membersbeing formed of a heat insulating structure so as to prevent atemperature drop of a portion of the discharge tube near electrodes ofthe discharge tube.

[0007] A light source device, according to the second aspect of thepresent invention, comprises a discharge tube, a reflector forreflecting a light radiated from the discharge tube, and support membersfor supporting the discharge tube to the reflector, the discharge tubebeing formed of a partially heat insulating structure so as to prevent atemperature drop of a portion of the discharge tube near electrodes ofthe discharge tube.

[0008] A light source device, according to the third aspect of thepresent invention, comprises a discharge tube, a reflector forreflecting a light radiated from the discharge tube, and support membersfor supporting the discharge tube to the reflector, the support membersbeing arranged at positions inward from ends of electrodes of thedischarge tube so as to prevent a temperature drop of a portion of thedischarge tube near electrodes of the discharge tube.

[0009] A light source device, according to the fourth aspect of thepresent invention, comprises a discharge tube, a reflector forreflecting a light radiated from the discharge tube, support members forsupporting the discharge tube to the reflector, and a heat conductionmember contacting a central portion of the discharge tube.

[0010] In these arrangements, generally, the operating life of thedischarge tube will end if the mercury contained in the discharge tubeis consumed. Consumption of mercury occurs in such a manner that gaseousmercury in the discharge tube reacts with particles of metal of theelectrodes (for example, Ni) caused by sputtering with electrons and isadhered to and captured by the inner surface of the discharge tube. Asufficiently large amount of mercury is usually inserted in thedischarge tube, it takes much time for mercury to be consumed and,therefore, the operating life of the discharge tube is guaranteed tosome extent.

[0011] However, there are several discharge tubes among many dischargetubes which have extremely short operating life. According to theinventor's study, the extremely short operating life is caused by thefollowing reason. That is, a portion of the discharge tube near theelectrodes is primarily a portion at which the largest amount of heat isgenerated and the temperature is higher, but in the structure in whichthe discharge tube is supported to the reflector by the support members,heat of the discharge tube is thermally conducted to the reflectorthrough the support members and further from the reflector to thehousing of the display device, so that the temperature of the portion ofthe discharge tube near the electrodes becomes the lowest within thedischarge tube. Also, the support members are arranged at positions nearthe electrodes of the discharge tube, the reflector is generally made ofmetal, and the support members are made of silicone so as to withstandthe high voltage applied to the electrodes. Therefore, heat of thedischarge tube is liable to be conducted to the reflector through thesupport members.

[0012] Mercury exists in the discharge tube in a gaseous state as wellas in a non-gaseous state (liquid or solid). The liquid mercury iscollected at the lowest temperature point in the discharge tube (becausea concentration gradient is produced because of a difference in asaturated vapor pressure due to a temperature difference, mercury isconveyed by diffusion). Particles of metal of the electrodes caused bysputtering with electrons are deposited on the thus collected liquidmercury, and produces a thin membrane on the liquid mercury. Thismembrane prevents the mercury from evaporating, and the amount of thegaseous mercury in the discharge tube is reduced. If the amount of thegaseous mercury is reduced, the discharge tube becomes dark and theoperating life thereof is short.

[0013] Accordingly, in the present invention, a shortened operationallife of the discharge tube is prevented by adopting the above-describedarrangements so that the portion of the discharge tube near theelectrodes of the discharge tube does not become the lowest temperaturepoint and so that the liquid mercury is not captured and enclosed by theparticles of metal of the sputtered electrodes, whereby the amount ofthe gaseous mercury is not reduced.

[0014] The above-described light source device can be used as a lightsource device of an information processing apparatus and a displaydevice.

[0015] Further, the present invention provides an information processingapparatus comprising a light source device and a light valve receiving alight emitted by the light source device, the light source deviceincluding a discharge tube, a reflector for reflecting a light radiatedfrom the discharge tube, support members for supporting the dischargetube to the reflector, and a layer of heat insulating material arrangedbetween the discharge tube and the support member or between the supportmember and the reflector.

[0016] Further, the present invention provides a display devicecomprising a light source device and a light valve receiving a lightilluminated by the light source device, the light source deviceincluding a discharge tube, a reflector for reflecting a light radiatedfrom the discharge tube, support members for supporting the dischargetube to the reflector, and a layer of heat insulating material arrangedbetween the discharge tube and the support member or between the supportmember and the reflector.

[0017] Further, the present invention provides a light source devicecomprising a discharge tube, a reflector for reflecting a light radiatedfrom the discharge tube, and support members for supporting thedischarge tube to the reflector, the reflector being made of a resin.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In the drawings:

[0019]FIG. 1 is a view showing the notebook type personal computerincluding the light source device according to the present invention;

[0020]FIG. 2 is a view showing the display device including the lightsource device of the present invention;

[0021]FIG. 3 is a plan view of the light guide plate and the lightsource device of the display device of FIG. 1;

[0022]FIG. 4 is a sectional view of the light guide plate and the lightsource device of FIG. 3;

[0023]FIG. 5 is a sectional view showing the discharge tube;

[0024]FIG. 6 is a sectional view of the light source device includingthe discharge tube and the reflector;

[0025]FIG. 7 is a sectional view of the light source device, taken alongthe line VII-VII in FIG. 6;

[0026]FIG. 8 is a sectional view of the light source device includingthe discharge tube and the reflector according to another example;

[0027]FIG. 9 is a sectional view of the support member of FIG. 8;

[0028]FIG. 10 is a sectional view of the light source device includingthe discharge tube and the reflector according to a further example;

[0029]FIG. 11 is a sectional view of the light source device includingthe discharge tube and the reflector according to a further example;

[0030]FIG. 12 is a sectional view of the light source device includingthe discharge tube and the reflector according to a further example;

[0031]FIG. 13 is a sectional view of the light source device includingthe discharge tube and the reflector according to a further example;

[0032]FIG. 14 is a sectional view of the light source device includingthe discharge tube and the reflector according to a further example; and

[0033]FIG. 15 is a sectional view of the light source device includingthe discharge tube and the reflector according to a further example.

BEST MODE FOR CARRYING OUT THE INVENTION

[0034] Embodiments of the present invention will be explainedhereinafter with reference to the accompanying drawings. FIG. 1 is aview showing the notebook type personal computer including the lightsource device according to the embodiment of the present invention, andFIG. 2 is a view showing the display device including the light sourcedevice according to the present invention.

[0035] In FIG. 1, the notebook type personal computer 1 comprises a body3 having a keyboard 2 and electronic circuits, and a display part 5having a display 4 such as a liquid crystal display device. The displaypart 5 has a light source device 18. The notebook type personal computer1 of FIG. 1 includes one light source device 18, but it is possible toarrange two light source devices 18, as in the case of the displaydevice 6 of FIG. 2.

[0036] In FIG. 2, the display device 6 comprises a body 8 having adisplay 7 such as a liquid crystal display device and electroniccircuits. The body 8 has light source devices 18. The display device 6of FIG. 2 includes two light source devices 18, but it is possible toarrange one light source device 18, as in the case of the notebook typepersonal computer 1 of FIG. 1.

[0037]FIG. 3 is a plan view of the light guide plate and the lightsource device of the display 4 of FIG. 1, and FIG. 4 is a sectional viewof the light guide plate and the light source device of FIG. 3. In FIGS.3 and 4, the display 4 includes a liquid crystal display panel 12 and abacklight 14. The backlight 14 includes a light guide plate 16, thelight source devices 18 arranged at the side of the light guide plate16, a scattering reflection plate 20 arranged below the light guideplate 16, and a scattering plate 22 arranged above the light guide plate16.

[0038] The light source device 18 comprises a discharge tube 24 and areflector 26. A part of the light emitted by the discharge tube 24 ismade directly incident to the light guide plate 16, and another part ofthe light outgoing from the discharge tube 24 is reflected by thereflector 26 to be made incident to the light guide plate 16. The lighttravels within the light guide plate 16, is reflected by the scatteringreflection plate 20 to leave the light guide plate 16 toward the liquidcrystal display panel 12, and is made incident to the liquid crystaldisplay panel 12 after being scattered by the scattering plate 22. Theliquid crystal display panel 12 forms an image, and the light suppliedfrom the light source device 14 illuminates the image formed by theliquid crystal display panel 12, so that a viewer can see a brightimage.

[0039]FIG. 5 is a sectional view showing the discharge tube 24, and FIG.6 is a sectional view showing the light source device 18 including thedischarge tube 24 and the reflector 26. FIG. 7 is a sectional view ofthe light source device 18, taken along the line VII-VII in FIG. 6. Thedischarge tube 24 comprises a cold-cathode tube called a fluorescentlamp. Electrodes 24A made of metal such as Ni or W are arranged in theends of the discharge tube 24. Lean gas (such as Ar or Ne) and mercury28 are inserted and sealed in the discharge tube 24, and a fluorescentmaterial is coated on the inner surface of the discharge tube 24. Thereflector 26 comprises an aluminum mirror, for example, and has across-sectional shape such a U-shape to cover the discharge tube 24.

[0040] Support members 25 are arranged on the discharge tube 24 near theelectrodes 24A for supporting the discharge tube 24 to the reflector 26.The inner surface of the support member 25 is in close contact with thedischarge tube 24, and the outer surface of the support member 25 is inclose contact with the reflector 26. A portion of the electrode 24A iswithin the discharge tube 24, and another portion of the electrode 24Aextends to the exterior of the discharge tube 24 through the end of thedischarge tube 24 and the end of the support member 25.

[0041] The support member 25 is formed of a heat insulating structure soas to prevent a temperature drop of a portion of the discharge tube 24near the electrode 24A. In this embodiment, the support member 25 ismade of a material having high heat insulating property and high voltagewithstanding property. For example, the support member 25 is made ofAramid fiber. The support member 25 can be made of glass wool.

[0042] In the structure in which the discharge tube 24 is supported bythe reflector 26 with the support members 25, there is a tendency thatheat of the discharge tube 24 is thermally conducted to the reflector 26through the support members 25, and further from the reflector 26 to thehousing of the display device, so that the temperature of a portion ofthe discharge tube 24 near the electrodes 24A may be reduced.

[0043] Conventional support members are made of silicone so as towithstand the high voltage applied to the electrodes, and the heat ofthe discharge tube 24 is thermally conducted to the reflector 26 throughthe support members 25, because silicone has a good heat conductivity,so that the temperature of the portion of the discharge tube 24 near theelectrodes 24A may be possibly reduced to the lowest value. Therefore,liquid mercury is collected at the portion of the discharge tube 24 nearthe electrodes 24A where the temperature is lowest, resulting in thereduction of the amount of gaseous mercury and a short life of thedischarge tube 24.

[0044] In the present invention, the support member 25 is formed of ahighly heat insulating material, so the heat of the discharge tube 24 isnot so mush thermally-conducted to the reflector 26 through the supportmembers 25, and the temperature of the portion of the discharge tube 24near the electrodes 24A is not reduced to the lowest value. The portionof the discharge tube 24 near the electrodes 24A is a portion at whichthe amount of the generated heat is primarily maximum and thetemperature is higher, and the position at which the temperature becomeslowest in the discharge tube 24 is shifted toward the center from theregion in which the support member 25 extends. Therefore, liquid mercuryis not collected at the portion of the discharge tube 24 near theelectrodes 24A.

[0045] On the other hand, metal of the electrodes 24A of the dischargetube 24 is sputtered with electrons during discharge and particles ofmetal of the electrodes 24A are deposited on the inner surface of thedischarge tube 24. The region in which particles of metal of theelectrodes 24A are deposited on the inner surface of the discharge tube24 is limited to the region within a restricted distance from the end ofthe electrode 24A. For example, in the case of the discharge tube 24having the diameter of 5 mm, the region in which particles of metal ofthe electrodes 24A are deposited on the inner surface of the dischargetube 24 is within approximately 10 mm from the end of the discharge tube24 or within 5 mm from the end of the electrode 24A.

[0046] Liquid mercury is not collected in the region in which particlesof metal of the electrodes 24A are deposited, so liquid mercury is notcaptured by particles of metal. Therefore, according to the presentinvention, most liquid mercury can continue to evaporate and the amountof gaseous mercury is not reduced, so the operating life of thedischarge tube 24 is not shortened.

[0047]FIG. 8 is a sectional view of the light source device 18 includingthe discharge tube 24 and the reflector 26 according to a modifiedembodiment, and FIG. 9 is a sectional view of the support member of FIG.8. Support members 25 are arranged on the discharge tube 24 near theelectrodes 24A for supporting the discharge tube 24 to the reflector 26.The support member 25 is formed of a heat insulating structure so as toprevent a temperature drop of a portion of the discharge tube 24 nearthe electrode 24A. In this embodiment, the support member 25 is made ofsilicone, similar to a conventional support member, but the supportmember 25 has a hollow portion 25B to realize a heat insulatingstructure. The operation of this embodiment is similar to that of theprevious embodiment.

[0048]FIG. 10 is a sectional view of the light source device 18including the discharge tube 24 and the reflector 26 (reflector 26 isomitted in FIG. 10) according to a modified embodiment. In thisembodiment, the discharge tube 24 is partially formed of a heatinsulating structure so as to prevent a temperature drop of a portion ofthe discharge tube 24 near the electrode 24A of the discharge tube 24.In other words, the end portion of the discharge tube 24 is formed in adouble-tube structure having an outer tube portion 24 o and an innertube portion 24 i, so that a heat insulation part comprising an airlayer or a vacuum layer is provided between the outer tube portion 240and the inner tube portion 24 i. The support member 25 is arrangedaround the outer tube portion 24 o and supports the discharge tube 24 tothe reflector 26. The operation of this embodiment is similar to that ofthe previous embodiment.

[0049]FIG. 11 is a sectional view of the light source device 18including the discharge tube 24 and the reflector 26 according to amodified embodiment. In this embodiment, the support members 25 arearranged at positions inward from the ends of electrodes 24A of thedischarge tube 24 so as to prevent a temperature drop of a portion ofthe discharge tube 24 near the electrode 24A of the discharge tube 24.As described above, the region in which particles of metal of theelectrodes 24A are deposited on the inner surface of the discharge tube24 is limited to the region within a restricted distance from the end ofthe electrode 24A. The support members 25 are arranged on the outside ofthe regions in which particles of metal of the electrodes 24A aredeposited (i.e., inward positions).

[0050] In this case, the support members 25 are not necessarily made ofa heat insulating material, and are made of silicone, for example.Therefore, the temperature is lowest at the portion of the dischargetube 24 where the support members 25 are located due to the thermalconduction through the support members 25, as described above. However,as the lowest temperature portion of the discharge tube 24 is out of theregion in which particles of metal of the electrodes 24A are depositedon the inner surface of the discharge tube 24, so liquid mercury is notcaptured by particles of metal. Therefore, according to the presentinvention, most liquid mercury can continue to evaporate and the amountof gaseous mercury is not reduced, so the operating life of thedischarge tube 24 is not shortened.

[0051]FIG. 12 is a sectional view of the light source device 18including the discharge tube 24 and the reflector 26 according to amodified embodiment. In this embodiment, the light source device 18comprises support members 25 arranged at positions near electrodes 24Aof the discharge tube 24 for supporting the discharge tube 24 to thereflector 26, and a heat conduction member 32 contacting a centralportion of the discharge tube 24. The support members 25 are made ofsilicone. The heat conduction member 32 is made of silicone havinghigher heat radiating property. Alternatively, it is possible to arrangefins on the heat conduction member 32 or to deliver cooling air from afan.

[0052] The heat conduction member 32 also contacts the reflector 26 andreleases the heat of the central portion of the discharge tube 24 to thereflector 26 to move the lowest temperature portion to the centralportion of the discharge tube 24. Therefore, liquid mercury is notcollected to a portion of the discharge tube 24 near the electrodes 24A,and liquid mercury is not captured by particles of metal. Therefore,according to the present invention, most liquid mercury can continue toevaporate and the amount of gaseous mercury is not reduced, so theoperating life of the discharge tube 24 is not shortened.

[0053] Also, by moving the lowest temperature point to the centrer ofthe discharge tube 24, mercury 28 evaporates mainly at the lowertemperature portion and resultant gaseous mercury diffuses in the wholedischarge tube 24. The diffused gaseous mercury also returns to thelower temperature portion. In this way, gaseous mercury is uniformlydistributed in the whole discharge tube 24, and the temperature and thepressure of gaseous mercury are substantially uniform in the wholedischarge tube 24. That is, it is possible to control the temperature ofgaseous mercury, by making the lower temperature point. The brightnessof light emitted by the discharge tube 24 becomes maximum at the optimumconcentration of gaseous mercury, and the corresponding temperature, inthe discharge tube 24, and the brightness of the light emitted by thedischarge tube 24 is lower than the maximum value if the concentrationof gaseous mercury is higher or lower than the optimum concentration orif the temperature in the discharge tube 24 is higher or lower than theoptimum value. In this embodiment, it is possible to acquire the maximumbrightness of the light emitted by the discharge tube 24, by moving thelower temperature point in the discharge tube 24 to thereby set thetemperature in the discharge tube 24 at or near the optimum value.

[0054]FIG. 13 is a sectional view of the light source device 18including the discharge tube 24 and the reflector 26 according to amodified embodiment. Support members 25 are arranged at positions nearthe electrodes 24A of the discharge tube 24 for supporting the dischargetube 24 to the reflector 26. A layer of heat insulating material (heatinsulating sheet) 34 is arranged between the discharge tube 24 and thereflector 26. The discharge tube 24 is attached to the reflector 26,with the layer of heat insulating material 34 bonded to the supportmember 25. The support member 25 is made of silicone as in theconventional case, and the layer of heat insulating material 34 is madeof meta-type Aramid fiber (Cornex from Teijin Corporation, for example).The support member 25 has a good heat conducting property, but the layerof heat insulating material 34 blocks the heat to thereby prevent theheat from escaping from the ends of the discharge tube 24 to thereflector 26. Therefore, a temperature drop of a portion of thedischarge tube 24 near the electrodes 24A is prevented. The operation ofthis embodiment is identical to that of the previous embodiments.

[0055]FIG. 14 is a sectional view of the light source device 18including the discharge tube 24 and the reflector 26 according to amodified embodiment. Support members 25 are arranged at positions nearthe electrodes 24A of the discharge tube 24 for supporting the dischargetube 24 to the reflector 26. A layer of heat insulating material (heatinsulating sheet) 34 is arranged between the discharge tube 24 and thesupport member 25. The support member 25 is made of silicone as in theconventional case, and the layer of heat insulating material 34 is madeof meta-type Aramid fiber (Cornex from Teijin Corporation, for example).The support member 25 has a good heat conducting property, but the layerof heat insulating material 34 blocks the heat to thereby prevent theheat from escaping from the ends of the discharge tube 24 to thereflector 26. Therefore, a temperature drop of a portion of thedischarge tube 24 near the electrodes 24A is prevented. The operation ofthis embodiment is identical to that of the previous embodiments.

[0056]FIG. 15 is a sectional view of the light source device 18including the discharge tube 24 and the reflector 26 according to amodified embodiment. In this embodiment, the reflector 26 is made of aheat insulating resin, for example, polycarbonate. Polycarbonate is apolyester resin of carbonic and polyhydric alcohol. Polycarbonate usingaromatic alcohol has properties such as a higher melting point (superiorto thermal stability), a higher mechanical strength, and a higherelectric insulation. A reflection layer 26A such as aluminum is coatedon the inner surface of the reflector 26 so that it does not overlapwith the support members 25. Therefore, the support member 25 has a goodheat conducting property, but the reflector 2.6 blocks the heat tothereby prevent the heat from escaping from the ends of the dischargetube 24 to the reflector 26 through the support members 25. Therefore, atemperature drop of a portion of the discharge tube 24 near theelectrodes 24A is prevented. The operation of this embodiment isidentical to that of the previous embodiments.

INDUSTRIAL APPLICABILITY

[0057] As explained above, according to the present invention, it ispossible to provide a light source device having a discharge tube havinga long operating life.

1. A light source device comprising a discharge tube, a reflector toreflect a light radiated from said discharge tube, and support membersto support said discharge tube to said reflector, said support membersbeing formed of a heat insulating structure so as to prevent atemperature drop of a portion of said discharge tube near electrodes ofsaid discharge tube.
 2. A light source device comprising a dischargetube, a reflector to reflect a light radiated from said discharge tube,and support members to support said discharge tube to said reflector,said discharge tube being formed of a partially heat insulatingstructure so as to prevent a temperature drop of a portion of saiddischarge tube near electrodes of said discharge tube.
 3. A light sourcedevice comprising a discharge tube, a reflector to reflect a lightradiated from said discharge tube, and support members to support saiddischarge tube to said reflector, said support members being arranged atpositions inward from ends of electrodes of said discharge tube so as toprevent a temperature drop of a portion of said discharge tube near theelectrodes of said discharge tube.
 4. A light source device comprising adischarge tube, a reflector to reflect a light radiated from saiddischarge tube, support members arranged at positions near electrodes ofsaid discharge tube to support said discharge tube to said reflector,and a heat conduction member contacting a central portion of saiddischarge tube.
 5. An information processing apparatus comprising alight source device and a light valve receiving a light emitted by saidlight source device, said light source device including a dischargetube, a reflector to reflect a light radiated from said discharge tube,support members to support said discharge tube to said reflector, and alayer of heat insulating material arranged between said discharge tubeand said support member or between said support member and saidreflector.
 6. A display device comprising a light source device and alight valve receiving light emitted by said light source device, saidlight source device including a discharge tube, a reflector to reflect alight radiated from said discharge tube, support members to support saiddischarge tube to said reflector, and a layer of heat insulatingmaterial arranged between said discharge tube and said support member orbetween said support member and said reflector.
 7. A light source devicecomprising a discharge tube, a reflector to reflect a light radiatedfrom said discharge tube, and support members to support said dischargetube to said reflector, said reflector being made of a resin.